Two-headed Hydra

Although the result is infinitely less terrifying than the gigantic, many-headed monster of Greek mythology, scientists have succeeded in coaxing the real-life
Hydra, a tiny freshwater polyp, into sprouting a second head using peptides. According to a report published in the November issue of the journal Genes & Development, the feat stems from their identification of a novel peptide
dubbed HEADY. The discovery sheds light on the mysterious process by which the head end of the organism¿s body axis is established during development. Earlier research had revealed a number of signaling peptides involved in axis specification
in flies, worms and mammals. The new study, conducted by Jan U. Lohmann and Thomas C. G. Bosch
of the University of Jena in Germany, demonstrates that they also play a key role in directing body axis formation in lower metazoans, or multicelled animals.

Because Hydra polyps are radially symmetrical, they have only one main axis¿one that goes in the top-bottom, or apical-basal, direction. In order to pinpoint HEADY¿s involvement in organizing the body plan, the researchers conducted
experiments in which they demonstrated that HEADY is expressed specifically in the apical end of the Hydra¿s body axis and that it is necessary for head formation in wild Hydra. In a third experiment, Hydra donor
tissue was treated with HEADY and labeled with fluorescent latex beads. Five days after it was transplanted into a host, the fluorescent tissue developed into a second head (right), thus manifesting HEADY¿s potent ability to
specify tissue fate. Taking these results into consideration, the authors conclude, "our data on the isolation and functional analysis of HEADY adds further support to the view that peptides have played a key role as developmental signals in metazoan evolution."